Elucidation of Glucose Homeostasis and Bioassay-Guided Fractionation of Fermented Blueberry Juice

Abstract

The liver and the muscle play an essential role in glucose homeostasis. Glucose-6-phosphatase (G-6Pase) and the glycogen synthase (GS) are the rate-limiting enzyme in gluconeogenesis pathway and glycogenogenesis pathway, respectively, in the liver. Recent studies reported that fermentation of blueberry juice (Vacciniumangustifolium; FBBJ) by Serratia vaccini bacterium possess strong antidiabetic potential both in vivo and in vitro. The purpose of this project is to elucidate the effects of FBBJ on glucose homeostasis in the liver and the muscle and to identify the active principles. FBBJ was fractionated using standard chromatography procedures. Confluent hepatic cell lines (H4IIE, HepG2) and muscle cell line (C2C12) were treated with maximal non-toxic concentrations of FBBJ, fractions or compounds. G-6Pase and GS activities were measured using the glucose oxidase method and a radioactive assay, respectively. Specific uptake of radioactive 2-Deoxy-D-glucose (2-DG*) into C2C12 was measured using a scintillation counter. Seven polyphenolic fractions were obtained from FBBJ fractionation (FBBJ.F1 – F7). FBBJ and its fractions FBBJ.F1 and FBBJ.F2 inhibited G-6Pase by 31%, 45% and 51%, activated GS by 2.3-, 2.2- and 2.3-folds and stimulated glucose uptake by 19%, 25% and 18%, respectively, as compared to DMSO. Further analysis of the active fractions yielded 4 compounds; compound 4(45.5μM) decreased G-6Pase activity by 54%, increased GS by 2-folds and stimulated glucose uptake by 44%. B FBBJ antidiabetic activity involves modulation of glucose homeostasis in the liver and the muscle. Bioassay-guided fractionation identified potential active compound, which will help standardize FBBJ.